It is known that apertured and/or embossed or non-apertured thermoplastic sheets or films have many useful applications. In disposable absorbent products, the apertured film permits the flow of liquid in the direction toward the absorbent materials in the disposable product, but reduces the possibility of fluid flow in the opposite direction. Embossed films with and without apertures are used in making products that have a cloth-like texture or appearance.
Methods for making such thermoplastic films include having a stationary drum with a perforated screen or molding element mounted on the outer surface of the drum. The screen is adapted to rotate freely on the surface of the drum. A vacuum chamber is employed beneath the screen or to create a pressure differential. As a film of thermoplastic material is passed over the screen, the pressure differential between the top surface of the film and the bottom surface of the film causes portions of the film to be pulled or flow into the perforations in the screen. A plurality of protuberances and/or apertures are formed in the film which correspond to the perforation pattern of the screen. One such method is described in Zimmerli, U.S. Pat. No. 3,054,148 reference.
A variety of methods and apparatuses, including particular types of perforating screens or rotatable molding elements have been developed over the years for particular perforation operations. Examples of these include U.S. Pat. Nos. 4,155,693, 4,252,516, 3,709,647, 4,151,240, 4,319,868 and 4,388,056. In U.S. Pat. No. 4,155,693, the screen comprises a series of perforated metal strips, preferably welded together to form a cylinder. U.S. Pat. No. 4,252,516 provides a screen having a series of hexagonal depressions with elliptical holes centered therein. U.S. Pat. No. 3,709,647 provides for a rotating vacuum-forming roll having a circulating cooling medium therein.
U.S. Pat. No. 4,151,240 provides a means for cooling the film after it has been perforated and debossed. U.S. Pat. No. 4,319,868 describes an apparatus for making a thermoplastic film having raised bosses with perforated tips. U.S. Pat. No. 4,388,056 discloses an air-laying drum having a honeycomb-type annular-shape frame including circumferentially extending ribs and transverse plates.
In certain instances, it is desired to produce films with protuberances (apertured or non-apertured) which can extend from the film at a substantially right angle to the surface of the film. Films with such right angle perforations provide a direct line of sight and a direct fluid path through the film. In certain other instances, the right angled protuberances are undesirable since the collected fluid remains visible through the perforations and a topsheet of the product. Accordingly, there is a need for film having characteristics which reduce the visible presence of the collected fluids.
The screen apparatus of the present invention is useful to produce three-dimensional films, wherein the desired protuberance geometry can extend through the film at an angle other than a substantially right angle to the surface of the film. The films can be utilized for protective clothing where fluids contact the surface of the film, such that the fluids do not have a direct path through the film. This non-flow through characteristic greatly improves the protective quality of the film or clothing.
Therefore, it is an object of the present invention to provide a screen apparatus for producing a three-dimensional film having a plurality of protuberances (apertured or non-apertured) of any desired configuration. Another object of the present invention is to provide a method for making such apparatus.
Another object of the present invention is to provide a thermoplastic three-dimensional film having protuberances or apertures which extend from the surface of the film at a right angle or an angle other than a right angle.
Other objects and advantages of the present invention will become more apparent from the reading of the description and drawings hereinafter.